Estimation of posterior corneal power for IOL calculation after myopic LASIK

Abstract

PURPOSE: To estimate the posterior corneal power for intraocular lens (IOL) calculation after myopic LASIK. METHODS: A retrospective study of 50 patients (92 eyes) who underwent uneventful myopic LASIK was conducted. Pre- and postoperative data (12 months) were collected including refraction and Orbscan II (Bausch & Lomb) for simulated keratometry (Sim K), central corneal thickness, and posterior corneal power. Statistical analysis was performed to determine the correlation between the postoperative posterior corneal power and other variables. An empirical formula was generated to predict the postoperative posterior corneal power. The net corneal power was calculated based on the new formula and Gaussian optics formula in an additional 31 eyes that underwent myopic LASIK and compared to the Orbscan total optical power map. The net corneal power was retrospectively applied to calculate the IOL power in an additional 10 patients who underwent cataract extraction after myopic LASIK. The back-calculation for emmetropic IOL power was performed and compared to the IOL power derived from the net corneal power. RESULTS: By using multiple linear regression, a formula to predict postoperative posterior corneal power can be computed from postoperative Sim K, central corneal thickness, and the amount of myopia treated with R2 of 0.63 (standard error = 0.25) (P<.05). The net corneal power was highly correlated to the total optical power (R 2=0.96); no statistically significant difference (paired t test) was noted (P>.05). The error of the IOL power derived from the net corneal power was -0.30±0.20 diopters. CONCLUSIONS: Corneal power after myopic LASIK can be estimated using postoperative Sim K, central corneal thickness, and the amount of myopia treated, which can be used for the assessment of IOL power after myopic LASIK.